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MAX6680MEE+

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17
MAX6680/MAX6681
To ensure valid extended data, read extended resolu-
tion temperature data using one of the following
approaches:
1) Put the MAX6680/MAX6681 into standby mode by
setting bit 6 of the Configuration register to 1. Initiate
a one-shot conversion using Send Byte command
0Fh. When this conversion is complete, read the
contents of the temperature data registers.
2) If the MAX6680/MAX6681 are in run mode, read the
Status register. If a conversion is in progress, the
BUSY bit is set to 1. Wait for the conversion to com-
plete as indicated by the BUSY bit being set to zero,
then read the temperature data registers.
Diode Fault Alarm
There is a continuity fault detector at DXP that detects
an open circuit between DXP and DXN, or a DXP short
to V
CC
, GND, or DXN. If an open or short circuit exists,
the External Temperature register is loaded with 1000
0000. Additionally, if the fault is an open circuit, bit 2
(OPEN) of the Status byte is set to 1 and the ALERT
condition is activated at the end of the conversion.
Immediately after power-on reset, the Status register
indicates that no fault is present until the end of the first
conversion.
Alarm Threshold Registers
Four registers store ALERT threshold values—one high-
temperature (T
HIGH
) and one low-temperature (T
LOW
)
register each for the local and remote channels. If
either measured temperature equals or exceeds the
corresponding ALERT threshold value, the ALERT out-
put is asserted.
The POR state of both ALERT T
HIGH
registers is 0111
1111 or +127°C and the POR state of T
LOW
registers is
1100 1001 or -55°C.
Two additional registers, RWOE and RWOI, store
remote and local alarm threshold data information cor-
responding to the OVERT output (see the
OVERT
Overtemperature Alarm section).
ALERT
The ALERT output operates in two modes—the typical
interrupt mode and comparator mode. The INT_SEL
input determines the mode. When INT_SEL is connect-
ed to V
CC
high, using a weak pullup resistor, or left
floating, the ALERT functions in the interrupt mode.
ALERT
Interrupt Mode
An ALERT interrupt occurs when the internal or external
temperature reading exceeds a high or low tempera-
ture limit (user programmed) or when the remote diode
is disconnected (for continuity fault detection). The
ALERT interrupt output signal is latched and can be
cleared only by either reading the Status register or by
successfully responding to an Alert Response address.
In both cases, the alert is cleared even if the fault con-
dition still exists, but is reasserted at the end of the next
conversion. The interrupt does not halt automatic con-
versions. The interrupt output pin is open drain so that
multiple devices can share a common interrupt line.
The interrupt rate never exceeds the conversion rate.
Comparator Mode
Connecting INT_SEL to ground operates the ALERT
output in comparator mode. In the comparator mode,
whenever the temperature of the remote or local temp
sensor goes outside the limits set by T
HIGH
or T
LOW
,
the ALERT output becomes inactive after the tempera-
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
10 ______________________________________________________________________________________
TEMP (°C)
LEGACY MODE
DIGITAL OUTPUT
EXTENDED
RANGE
DIGITAL OUTPUT
127.00 0111 1111 0111 1111
25 0001 1001 0001 1001
1 0000 0001 0000 0001
0.00 0000 0000 0000 0000
-1 0000 0000 1111 1111
-25 0000 0000 1110 0111
-64 0000 0000 1000 0000
Diode Fault
(Short or
Open)
1000 0000 1000 0000
Table 2. Data Format (Two’s Complement)
FRACTIONAL
TEMPERATURE
CONTENTS OF
EXTENDED REGISTER
0.000 000X XXXX
0.125 001X XXXX
0.250 010X XXXX
0.375 011X XXXX
0.500 100X XXXX
0.625 101X XXXX
0.750 110X XXXX
0.875 111X XXXX
Table 3. Extended Resolution Register
Note: Extended mode applies only for conversion rates of 4Hz
and slower.
ture returns within the limits. An open diode also sets
this output.
Alert Response Address
The SMBus Alert Response interrupt pointer provides
quick fault identification for simple slave devices that
lack the complex, expensive logic needed to be a bus
master. Upon receiving an ALERT interrupt signal, the
host master can broadcast a Receive Byte transmission
to the Alert Response slave address (see the Slave
Addresses section). Then, any slave device that gener-
ated an interrupt, attempts to identify itself by putting its
own address on the bus (Table 4).
The Alert Response can activate several different slave
devices simultaneously, similar to the I
2
C General Call.
If more than one slave attempts to respond, bus arbitra-
tion rules apply, and the device with the lower address
code wins. The losing device does not generate an
acknowledge and continues to hold the ALERT line low
until cleared. (The conditions for clearing an alert vary
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
______________________________________________________________________________________ 11
SMBCLK
AB CD
E
FG H
I
J
K
SMBDATA
t
SU:STA
t
HD:STA
t
LOW
t
HIGH
t
SU:DAT
t
HD:DAT
t
SU:STO
t
BUF
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
L
M
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
I = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
Figure 4. SMBus Write Timing Diagram
Figure 5. SMBus Read Timing Diagram
MAX6680/MAX6681
depending on the type of slave device.) Successful
completion of the Alert Response protocol clears the
interrupt latch, provided the condition that caused the
alert no longer exists. If the condition still exists, the
device reasserts the ALERT interrupt at the end of the
next conversion.
OVERT
Overtemperature Alarm
Two registers, RWOE and RWOI, store remote and local
alarm threshold data corresponding to the OVERT out-
put. The values stored in these registers are high-tem-
perature thresholds. If any one of the measured
temperatures equals or exceeds the corresponding
alarm threshold value, an OVERT output is asserted.
The overtemperature thresholds are both hardware and
software programmable. The overtemperature thresh-
olds can be hardware programmed by pin strapping
CRIT0 and CRIT1. Use Table 4 to set the desired
remote and local threshold temperatures. Upon POR or
driving the RESET pin high, the Overtemperature regis-
ter takes on the hardware-programmed values.
Afterward, any write to the Overtemperature registers
overwrites the hardware-programmable values.
OVERT always operates in comparator mode and is
asserted when the temperature rises to a value pro-
grammed in the appropriate threshold register. It is
deasserted when the temperature drops below this
threshold minus the programmed value in the Hysteresis
(HYST) register. An OVERT output can be used to acti-
vate a cooling fan, send a warning, initiate clock throt-
tling, or trigger a system shutdown to prevent component
damage. The HYST byte sets the amount of hysteresis
to deassert the OVERT output. The data format for the
HYST byte is 7 bits + sign with 1°C resolution. Bit 7 of
the HYST register should always be zero.
Command Byte Functions
The 8-bit Command Byte register (Table 5) is the mas-
ter index that points to the various other registers within
the MAX6680/MAX6681. This register’s POR state is
0000 0000, so a Receive Byte transmission (a protocol
that lacks the command byte) occurring immediately
after POR returns the current local temperature data.
One Shot
The One-Shot command immediately forces a new con-
version cycle to begin. If the One-Shot command is
received when the MAX6680/MAX6681 is in software
standby mode (RUN/STOP bit = 1), a new conversion is
begun, after which the device returns to standby mode.
If a conversion is in progress when a One-Shot com-
mand is received, the command is ignored. If a One-Shot
command is received in autoconvert mode (RUN/STOP
bit = 0) between conversions, a new conversion
begins, the conversion rate timer is reset, and the next
automatic conversion takes place after a full delay
elapses.
Configuration Byte Functions
The Configuration Byte register, Table 6, is a read-write
register with several functions. Bit 7 is used to mask
(disable) ALERT interrupts. Bit 6 puts the device into
software standby mode (STOP) or autonomous (RUN)
mode. Bit 5 selects the type of external junction (set to
0 for a substrate PNP on an IC or set to 1 for a discrete
diode-connected transistor) for optimized measure-
ments. Bit 4 selects the extended temperature mea-
surement for the remote sensor. If high, the temperature
data is available as 10 bits + sign with a 0.125°C reso-
lution, otherwise, 7 bits + sign with 1°C resolution. Bit 4
extends the temperature range of the remote and local
temperature sensor to -64°C. Bit 2 disables the SMBus
timeout, as well as the Alert Response. Bit 1 provides a
software reset from the SMBus. Bit 0 is reserved and
returns a zero when read.
Status Byte Functions
The status byte (Table 7) indicates which (if any) tem-
perature thresholds have been exceeded. This byte
also indicates whether the ADC is converting and if
there is an open-circuit fault detected with the external
sense junction. After POR, the normal state of the regis-
ters’ bits is zero, assuming no alert or overtemperature
conditions are present. When operating the
MAX6680/MAX6681 in ALERT interrupt mode, bits 2
through 6 of the Status register are cleared by any suc-
cessful read of the Status register, unless the fault per-
sists. The ALERT output follows the status flag bit. Both
are cleared when successfully read, but if the condition
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
12 ______________________________________________________________________________________
OVERT THRESHOLD (°C)
CRIT1 CRIT0
REMOTE LOCAL
GND GND +85 +70
GND Open +90 +75
GND V
CC
+95 +80
Open GND +100 +85
Open Open +105 +90
Open V
CC
+110 +95
V
CC
GND +115 +100
V
CC
Open +120 +105
V
CC
V
CC
+125 +110
Table 4. OVERT Temperature Threshold
Programming
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17

MAX6680MEE+

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Buy MAX6680MEE+
Manufacturer:
Maxim Integrated
Description:
Board Mount Temperature Sensors Fail-Safe Temperature Sensor
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